Patent GB-375339-A (GB)
Title: Improvements in synchronous electric motors
IPC: H02K19/10
Filed: 1931-01-19
Abstract: 375,339. Distant control systems. WALTON, G. W., 2, Dean Street, London. Jan. 19, 1931, No. 1799. [Class 40 (i).] A motor adapted to run in synchronism with electrical impulses has uniformly spaced poles of substantially the same polar arc on the rotor and stator, the poles on the stator or rotor or both being adapted for simultaneous energization to the same extent, the number of stator and rotor poles being different and not in integral multiple relationship and the number thereof and the polar arcs being so selected that a change of total engaged pole area takes place as the rotor rotates. Figs. 1A and 1B show a homopolar form of motor having a stator 1, a rotor 5, and a single stationary exciting coil 4. The minimum speed of this motor in revolutions per second is given by the formula Sm = F/M where F is the number of impulses per second and M the least common multiple of the number of stator and rotor poles. In general, the speed is given by the formula S = AF/M where A is an integer depending on the number of polar coincidences skipped between successive current impulses. A second rotor co-operating with additional stator poles may be arranged at the other end of the motor, in which case the stator or rotor poles at the two ends are displaced relatively to each other. A motor similar to that shown in Fig. 1B is described having eleven stator poles and seven rotor poles so that when connected to a 50 cycle supply, the speed will be 77 71/77 revolutions per minute, i.e. a speed approximating to that required for the direct drive of gramophones. When pure alternating current is supplied, each cycle represents two impulses, but continuous current may be supplied to the coil 4 or to an additional coil, or permanent magnets may be fitted whereby each cycle represents one impulse. Fig. 4B shows a non-homopolar form giving the same speed as that shown in Fig. 1B. If the motor is required to be self-starting, the rotor may be provided with a squirrel cage winding and the stator may have shaded poles or additional poles carrying winding of an auxiliary phase. It is explained in the Specification that to permit operation of the motor, a change of overlapping area between stator and rotor is necessary as the rotor rotates. For this purpose, the angles subtended by the pole arcs at the axis should be other than 360n‹/M where n is any integer and M the L.C.M. of the pole numbers. Preferably the angle is made less than 180‹/M or equal to an odd integral multiple of 180‹/M. Fig. 7B shows a motor for specially low speeds comprising a stator 1, a rotor 5 and an intermediate rotor or spinner 12 having poles co-operating with the stator and rotor poles. By arranging that the rotor and spinner rotate in opposite directions, very low absolute speeds of the rotor may be obtained. More than one spinner in tandem may be employed. The motors described may be used as generators. A generator may be connected to a motor to constitute a remote control or remote indication system. In a simple form two machines of the type shown in Figs. 1A and 1B are connected together, but with this arrangement, all movements of the generator rotor must be in the same direction and the distance moved must correspond to the angle of movement produced by one impulse or any multiple thereof. Also the generator rotor must not be moved less than a certain speed. Fig. 9 shows a double machine having a magnetic wall 19 between the two halves of the motor. The coils 4, 4a are connected to the coils of a similar machine as shown in Fig. 10A and alternating current is applied to the terminals 22, 23. The self-starting arrangements are such that the two rotors of each motor tend to rotate in opposite directions so that normally there will be no movement of the rotors. If the rotor of one machine, say 20 be rotated, different frequencies will be generated in the coils 4, 4a which acting on the coils of the distant motor 21 cause the rotor thereof to turn. Two different frequencies may be used, one applied to the terminals 22, 23 and the other to the terminals 23, 27. The number of poles of the two halves of each motor are so arranged that the two rotors tend to rotate in opposite directions at the same speed. Fig. 10B shows an alternative connection of the two machines. Fig. 10c shows a further connection in which two line wires only are necessary. Circuits 24 containing inductance and capacity are connected as shown to the coils 4, 4a and the two energizing frequencies are applied as before to the terminals 22, 23, 27. By suitable choice of the inductance and capacity of the circuits 24, there will be a predominance of one frequency in the coils 4 and a predominance of the other frequency in the coils 4a. In the arrangements described movement can only take place by steps. Fig. 11 shows an improved arrangement whereby movements of any amount can be transmitted. Three coils 4, 4a, 4b are separated by magnetic walls 19, 25 and spinners 12, 12a are arranged to rotate continuously in opposite directions at the same speed. Accordingly there is no tendency for the rotor 5 to rotate and if the number of poles on the outer peripheries of the two spinners are equal and also the numbers of poles at the two ends of the stator 1, equal frequencies will be generated in the coils 4a, 4b which may be connected to the corresponding coils of a distant motor. Movement of the rotor 5 causes one spinner to advance and the other to retard whereby frequencies will be generated in the coils 4a, 4b and the movement is repeated by the rotor of the distant motor. If the outer poles of the spinners 12, 12a are different in number, different frequencies will be generated in the coils 4a, 4b, when the rotor is at rest and the two machines may be connected together as shown in Fig. 12, parallel circuits 26 containing inductance and capacity being connected to the coils 4, 4a, 4b.